@aqua the hedgie: wait, just how long have you been using this sprite sheet?
Anyway.

well, now that i look at it up close in paint. you might need to fix the shading on all of it. its mostly the shading on the shirt and pants, you seem to be shading with the light source inside of him. I noticed this same problem with Uchi the Ocelot. you might want to establish a light source and attempt to stick with it.

You may want to change those shoes too, its kinda seems kinda lazy when you keep them as sonic's shoes only colored something different.

The Clothes also seem to grow and shrink in size. heres a couple of examples of what i mean.

http://prntscr.com/bgm2ut

http://prntscr.com/bgm390

Now, I sorta prepared a small sprite covering some of the ideas i discussed here. I have not sprited any sonic stuff in awhile, so please excuse any mistakes i may have made.
its 100x in case you want to use it as a starting point. it even has 2 versions of the pants. a version with the pants endings near the socks. and another with pants covering the socks.

@noiise: I didn't see your edit when I commented I never said anything about how you couldn't judge it so go ahead and criticise it, I just look past it due to it existing during an awkward time on the internet. Anyway I still don't see the point in adding anime characters to a sprite comment.